This study was conducted to investigate biological substrates of pathological gambling. We found indices of increased central nervous system noradrenergic activity. Also, depressed gamblers showed evidence of abnormal glucose homeostasis. Furthermore, indices of noradrenergic activity correlated significantly with extraversion scores on the Eysenck personality questionnaire suggesting that biological abnormality in gamblers may manifest itself by an effect on personality. In a study of GABA we found no difference in CSF levels between gamblers and controls or between depressed and non-depressed gamblers.